Cooling tower water treatment system

ABSTRACT

A cooling tower water treatment system removes contaminants include chlorine, calcium carbonate as calcite, and microorganisms from water in the system with redox media in a fluidized bed. The treatment system includes a treatment bed, in the form of a column, having a reaction chamber of a first diameter and a retention chamber of a second diameter, the second diameter being greater than the first diameter. Redox media, in the reaction chamber, is fluidized by water flowing in a direction countercurrent to gravity and is held in place, without the use of screens or filters, by a reduction in flow rate of the fluidizing media resulting from the larger diameter of the retention chamber. Preferably, the treatment system includes a physical filtration unit, such as an automatic backwashing sand filter, to prevent entry of particulates and scale into the reaction chamber.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to fluid treatment systems forindustrial use, and more particularly, to an improved cooling towerwater treatment system using redox media.

2. Description of the Related Art

Water is the most commonly used medium for removing heat from industrialequipment. Water has excellent heat transfer capability which isreversible so that the water can be cooled and reused. Typically, wateris recycled by the use of a cooling tower which allows a portion of thewater to be evaporated. Since water is rarely pure, contaminants in thewater are concentrated during the evaporation process. Concentration ofthe contaminants leads to multiple problems such as scaling, corrosionand fouling by algae, bacteria, and fungi, the treatment of whichrequire the use of chemicals and/or frequent maintenance.

In the past, water was typically treated with chemical conditioners tocontrol scaling, corrosion and biofouling. Chelators and complexers wereadded to control the formation of scale, inhibitors were added tocontrol corrosion, and biocides were added to control biofouling. Inaddition to the foregoing, other additives, such as buffers and pHcontrol additives are frequently used. The use of these chemicals addsexpense, increases effort to monitor and maintain appropriate chemicallevels, and creates disposal problems. Non-chemical systems have beendeveloped, such as magnetic systems and ozone generators, but these haveproven to be expensive and, at best, only marginally effective. Ozonesystems, for example, have a beneficial effect on the control ofbiofouling, but have a limited effect on the control of scale formationand corrosion protection.

A unique oxidation/reduction (redox) media has been discovered fortreating water by the galvanic reaction that results when the watercontacts bimetallic redox media. The bimetallic alloy used in the mediafor water treatment is preferably a high purity alloy of copper and zincin an appropriate ratio. The redox media is described more particularly,for example, in U.S. Pat. Nos. 5,510,034; 5,433,856; and relatedpatents. Redox potential (ORP) is a measure of the readiness to partwith electrons, and is measured in millivolts (mV). Zinc is morereactive than copper and is more electropositive. In the preferred redoxfilter media, copper is the permanent cathode and zinc is thesacrificial anode. A single pass through copper-zinc redox filter mediarapidly changes the redox potential of water from +200 mV to -500 mV.This change has a dramatic effect on most bacteriologic, solubility, andionic reactions. The redox media can remove dissolved gases such aschlorine, hydrogen sulfide and methane. It can also remove virtually anysoluble heavy metal, help prevent mineral scale accumulation and reducelevels of microorganisms.

More specifically, when cooling tower water is exposed to the redoxmedia, the flow of electrons alters the crystalline structure of thescale-forming compounds. The most common scale-forming compound iscalcium carbonate or calcite. When combined with carbon dioxidedissolved from the air, and exposed to heat, calcite is deposited in theheat exchangers, pipes, pumps, reservoirs, and towers used in thecooling system. Left uncontrolled, calcite will continue to grow uponitself until a thick layer of scale is formed. A 0.1" thick deposit ofcalcite, for example, will reduce the heat transfer ability of a heatexchange by about 40%. The modification of ORP produced by the redoxmedia causes the calcium to precipitate as fine particles of a carbonatecompound which is spherical or rod-shaped with rounded edges. Unlike thecoarse crystalline calcite scale, the carbonate precipitate cannot growupon itself and can be removed by filtration.

The medium controls biofouling by two mechanisms. The ORP changeproduced by contact with the media results in an electrolytic fieldwhich most microorganisms cannot survive. Second, hydroxyl radicals andperoxides are formed from some of the water molecules which alsoadversely impact microorganisms. Finally, the corrosion of metallicsurfaces is mitigated by the stabilization of pH to non-corrosivealkaline levels of between 8.0 and 8.5 through the generation ofhydroxyl radicals by the redox media. Additionally, the negative impacton bacterial growth prevents the generation of organic acids by thebacteria.

Despite these advantages, the use of the aforementioned redox media hasbeen accompanied by the several disadvantages. In typical prior artsystems, the redox media is supplied in a form similar to steel wool.This material is formed around a mandrel. Water flows from the outsideof the chamber, through the media, and through the mandrel. In anotherembodiment, the redox media is supplied in the form of a foam-likeproduct which has been formed into discs. The water flows through aseries of these discs for the appropriate contact time. The wool andfoam products, being held in a static position, become clogged over timewith particulate matter which is precipitated out of the water. Not onlydoes this lead to premature replacement of the media, but over time asclogging occurs, the surface area is reduced and flow is restricted. Asa result of this deterioration, performance is reduced and the problemsrelating to scale, biofouling, and corrosion can recur.

In order to overcome the foregoing problem, a granular media has beenused with a downflow pattern in a pressure vessel. While this alsoresults in a buildup of trapped particulates, periodic backwashingallows their removal. This system is an improvement over the wool andfoam systems described hereinabove where the media is permanentlyfouled, but results in diminished performance between backwashingcycles. Another disadvantage of this system is the loss of media due toflow rate of backwashing necessary for particle removal.

It is, therefore, an object of this invention to provide a cooling towertreatment system which does not rely on chemicals for conditioning thecooling water and is inexpensive and simple to maintain.

It is another object of this invention to provide a cooling tower watertreatment system which uses redox media efficiently without significantloss of performance between backwashing cycles.

It is also an object of this invention to provide a cooling towertreatment system which maximizes the life of the redox media and systemcomponents.

It is still a further object of this invention to provide a coolingtower treatment system which exhibits consistent performance levels overits lifetime.

SUMMARY OF THE INVENTION

The foregoing and other objects are achieved by this invention whichprovides a device for treating fluids, such as water from a coolingtower. The device includes a treatment bed wherein the fluid is broughtinto contact with treating media, preferably redox media in a course,granular form. Water, or other fluid to be treated, flows upward, orcountercurrent to the effect of gravity on the treating media, through alower portion of the treatment bed, or the reaction chamber, fluidizingthe treating media contained therein so that particulates of foreignmaterial are not trapped in the media. The treatment bed has an upperportion, or retention chamber, which is greater in diameter than thelower portion, so that the flow velocity of the water through the upperportion is reduced. This prevents media loss without the necessity ofusing a filter or other restraining means which could clog or otherwiseimpede the flow.

The treating media is provided in a particulate form so that it can befluidized by the flow of a liquid. In preferred embodiments, thetreating media is redox media which is granular and comprises metalshaving a favorable redox potential relative to the contaminants in thefluid to be treated. In the case of cooling tower water, the expectedcontaminants include chlorine, calcium carbonate as calcite, andmicroorganisms. Appropriate metals include aluminum, steel, zinc, tin,or copper in admixture or, preferably, as alloys. A preferred alloy is amixture of copper and zinc.

In a specific preferred embodiment, the redox medium is granular highpurity copper/zinc alloy in a 50:50 ratio atomized to have irregularlysized and shaped particles (US mesh screen size -10 to +100) sold underthe mark KDF 55 by KDF Fluid Treatments, Inc., Three Rivers, Mich.

As a further advantage of the present system, the granular redox mediahas life of at least a year. Should the media become fouled by oils orgrease, its performance can be restored by washing with a milddetergent. This washing can be accomplished by recirculating thedetergent solution through the system followed by rinsing with freshwater. Further, when exhausted, redox media is 100% recyclable throughcurrent scrap metal recycling systems.

In preferred embodiments, the device of the present invention includes aphysical filter which is placed in the system, prior to the treatmentbed, to prevent entry of particulates, precipitated material and scaleinto the fluidized bed of the reaction chamber. For example, themanufacturing process for granular redox media results in particles ofvarious sizes and shapes. The media is screened, but a significantamount of fines and flakes of low density still remain. During initialstart-up, many of these particles escape into the system. Since a topscreen in the column is impractical, as discussed above, any fines orflakes escaping into the system will be trapped by the filter.

In a preferred embodiment of the invention, the filter is a sand filter.In a particularly preferred embodiment, the sand filter is an automaticbackwashing sand filtration unit having a stainless steel filterchamber, self-priming pump, automatic multiport valve assemblies, andcoarse particle screen. The backwash cycle is dependent on pressuredifferential.

The bed is fluidized by contacting the treating media with a fluid in acountercurrent flow, specifically in an ascending manner against theforce of gravity. The flow of fluidizing medium, which in the presentexample is the fluid to be treated, is at a velocity ranging from thatrequired to fluidize the bed to that which will destabilize the bed, orcause back-mixing, channeling, or other turbulence. The maximum flowrate, however, is determined by the desired contact time of the fluidbeing treated with the treating media. In preferred embodiments, thefluid velocity may range from about 5 gal/min. to 20 gal/min. through asingle column. In a cooling tower water treatment system embodiment, thereservoir water is preferably recirculated every 60 to 90 minutes.Typically, a treatment system comprises from one to four columns inparallel, but the system can be adapted to handle any number of columnsrequired to control the flow rate through the treating media to thatrequired for efficient removal of contaminants. In addition, the columnsmay be designed to accommodate flows greater than 20 gpm byproportionally sizing the upper and lower chambers. The number ofcolumns is based on the volume of water in the reservoir.

A typical cooling tower water treatment system in accordance with thepresent invention comprises a heat exchanger, a cooling tower, areservoir, and a treatment system. The treatment system includes afiltration unit for receiving water from the reservoir and a treatmentbed for receiving filtered water from the filtration unit. The treatmentbed may comprise one or more reaction columns, each column having topand bottom chamber portions. Of course, in operation, the columnscontain fluidized redox media which is retained in the bottom reactionchamber portion by the upper retention chamber portion as describedhereinabove. Although the embodiments described herein are in the formof a conventional cylindrical column, other configurations are withinthe contemplation of the invention.

In a method embodiment of the invention, a process of treating a fluidcomprises filtering the fluid to remove particulates and treating thefiltered fluid by contact with a treating, or redox, media. The redoxmedia is contained in a lower reaction chamber of a treatment bed andheld in place hydrodynamically by a reduction in flow rate in an upperretention chamber of the treatment bed having a diameter which is largerthan the diameter of the reaction chamber. The redox media is fluidizedby the pumping filtered fluid through the media in a directioncountercurrent to the effect of gravity at a velocity sufficient tofluidize the media but not in excess of a velocity which would permitadequate contact time for reaction.

Because no additional chemicals are added to the water in the system,some of the constituents are actually precipitated from the water, thetotal dissolved solids (TDS) are actually reduced while the systemtolerance for TDS is increased. Since TDS mandates blowdown, thefrequency of blowdown is reduced. Moreover, the blowdown water isenvironmentally safe, containing only the constituents that are presentin the make-up water. A small amount of dissolved sacrificial zinc maybe present in the blowdown water, but tests have demonstrated that thezinc levels are well within the EPA maximum allowable limits for potablewater.

Advantageously, treating cooling water with the redox media andsubsequent filtration, in accordance with the invention, will endcalcium hardness and prevent scale from forming. Over time, existingscale in a retrofit system will be removed.

Tests have confirmed that performance of the treatment bed is maintainedat a steady level. Periodic visual inspection of heat exchangers,piping, and cooling tower surfaces have shown that no additional scaleis formed and that previously existing scale is gradually removed.Moreover, water test data has shown that contaminant levels such as TDS,pH, alkalinity, calcium hardness, and heavy metals achieve steadyequilibrium levels within 4 weeks of initial system operation. Moreover,tests have confirmed, that the equilibrium levels remain relativelyconstant over a 15 month period.

BRIEF DESCRIPTION OF THE DRAWINGS

Comprehension of the invention is facilitated by reading the followingdetailed description, in conjunction with the annexed drawing, in which:

FIG. 1 is a schematic representation of a cooling tower treatment systemin accordance with the present invention; and

FIG. 2 is an exploded representation of a treatment bed in accordancewith the present invention.

DETAILED DESCRIPTION

FIG. 1 is a schematic representation of a cooling tower treatment systemin accordance with the present invention. A typical cooling towersystem, portions of which are illustrated in FIG. 1, includes areservoir 11 to hold a supply of reservoir water 14, a distributionpiping network, pumps (e.g., 16, 17, 18), a heat exchanger 15, andcooling tower 12. Cooling tower 12 has a large surface area over whichwarm water cascades. Fans, such as fan 13, move air over the cascadingwater to facilitate lowering the temperature through evaporation. Thetower discharge water returns to reservoir 11 for re-use. In many cases,the tower, and sometimes the reservoir, are located outside where theyare exposed to sunlight and airborne contaminants. This creates an idealenvironment for the growth of algae, bacteria, and fungi resulting inbiofouling. As algae grows and dies, organic acids are created whichcontribute to corrosion of metallic surfaces. Moreover, as waterevaporates, dissolved solids increase as the volume of water isdecreased. Coupled with the heat of the water returning from the heatexchanger, it is common for scale, typically in the form of calcite, toform throughout the system. Heating efficiency is significantly reducedas calcite scale forms on the surface of the heat exchangers.

In order to mitigate the aforementioned problems, a portion of the waterin reservoir 11 is directed through fluid treatment system 10 by pump16. Reservoir 11, in this embodiment, contains reservoir watercomprising warm water returned from heat exchanger 15, cool waterdischarged from cooling tower 12, and treated water received fromtreatment system 10.

In the specific embodiment illustrated in FIG. 1, treatment system 1)comprises a filtration unit (30) and a treatment bed 20 which is in theform of a column. The filtration unit is a sand filtration assembly inpreferred embodiments. Referring to FIG. 1, sand filtration assembly 30comprises a vessel 31 for holding sand filter media 32. Reservoir waterdischarged through reservoir outlet 9 enters filtration assembly 30 atfiltration unit inlet 33. In the embodiment shown, three way valves 34and 35 control the direction of flow of water through the filtrationassembly for normal operation and backwash cycles. In normal operation,valves 34 and 35 are opened so that reservoir water is directed into thevessel through filter vessel inlet 38 and into feed distributor 37. Feeddistributor 37 disperses reservoir water on the top of sand filter media32. Particulates and scale are trapped by the sand as the water flowsdownward through the filter vessel. Filtered water exits the vessel atfiltration unit outlet 36 and enters treatment bed inlet 6 through valve35.

Periodically, valves 34 and 35 operate to create a backwash cycle. Inthe backwash cycle, reservoir water is directed into the filtrationvessel though filtration unit outlet 36. Water travels upward throughsand filter media 32, washing trapped particulates from the surface ofthe filter media, and exits the filter vessel at filter vessel inlet 38through valve 34 to a backwash drain (not shown). In a preferredembodiment, the sand filter assembly automatically cycles into backwashwhen the pressure in the filter vessel exceeds a certain value. In thismanner, the system continuously receives water from the reservoir andcooling tower yet maintains itself free from build-up of particulates,both in filtration assembly 30 and in the treatment bed 201 since onlyfiltered reservoir water enters treatment bed inlet 6.

Treatment bed 20 comprises a reaction chamber 3 of a first diameter (d₁)and a retention chamber 4 of a second diameter (d₂). The value of d₂ isgreater than the value of d₁ so that fluid flowing from reaction chamber3 loses velocity when it enters retention chamber 4. A particulatetreating media 5, which in preferred embodiments is redox media, iscontained in reaction chamber 3 and is fluidized by the flow ofreservoir water pumped into treatment bed 20 in a directioncountercurrent to the flow of gravity. As shown in FIG. 1, reservoirwater is pumped into treatment bed 20 through treatment bed inlet 6 andout through treatment system outlet 7. The fluidized media remains inreaction chamber 3 due to the decreased velocity of the water inretention bed 4 without the necessity of mechanical means, such as ascreen or filter, which would be subject to clogging. The treated waterexits treatment bed 20 and re-enters reservoir 11 through reservoirinlet 8.

Treatment bed 20 is shown in greater detail in the explodedrepresentation of FIG. 2 where elements common to FIG. 1 retain the samereference numerals. Referring to FIG. 2, a distribution manifold 31having a plurality of distribution orifices 32 distributes waterentering treatment bed 20 through treatment bed inlet 6 across thebottom of the column. Proper distribution of liquid at the bottom of thebed facilitates uniform fluidization of redox media (not shown in thisfigure) in reaction chamber 3. Media retainer screen 33 supports theredox media. Reaction chamber 3, having diameter d₁, is coupled toretention chamber 4, having diameter d₂, by reducing coupling 34.Treatment system outlet 7 is at the top of the column and dischargestreated water into reservoir inlet 8.

In a specific illustrative embodiment of the type shown in FIG. 2,reaction chamber 3 has an overall dimension of 6" in diameter by 24" inheight. The chamber volume is 678 cubic inches (0.39 cubic feet). If theflow rate of water entering treatment bed inlet 6 is 20 gallons perminute, the flow velocity through reaction chamber 3 is 0.71 gallons perminute per square foot of surface area. Retention chamber 4, on theother hand, has an overall dimension of 8" in diameter by 24" in height.The resulting chamber volume is 1,206 cubic inches (0.70 cubic feet).For a flow rate of 20 gallons per minute, the flow velocity throughretention chamber 4 is 0.40 gallons per minute per square foot ofsurface area. About 43 pounds of redox media has a volume of 336 cubicinches before fluidization which expands the volume of the redox mediato about 504 cubic inches.

Pumps 16-18 create the flow of water in the direction of the arrows. Theflow rate is controlled by flow regulators. In an illustrativeembodiment, the flow is adjusted by a gate valve in response to a paddlewheel flow sensor with an indicator. Contact time with the redox mediaaffects the speed and degree of removal of unwanted contaminants.Contact time can be adjusted by using smaller mesh granulated redoxmedia and/or by reducing the fluid flow rate.

Returning to the water cooling tower system shown in FIG. 1, the treatedwater exits treatment system 10 at treatment system outlet 7 and returnsto reservoir 11 through reservoir inlet 8. The reservoir water isdischarged through reservoir outlet 23 and into cooling tower inlet 24where it is cooled and returned through reservoir inlet 25. The cooledwater is discharged through reservoir outlet 22 into heat exchangerinlet 19. Warm water from the heat exchanger returns to the reservoirfrom heat exchanger outlet 21 through reservoir inlet 26.

Of course, the system shown in FIG. 1 is for the purposes ofillustration only and is not intended to be limiting. For example, thefluid treatment system 10 may comprise multiple columns. In this case,the treatment bed inlet 6 goes to a fluid distribution manifold (notshown) having multiple outlets for each column. Flow and pressuresensing meters and/or regulators and valves can be dispersed throughoutthe system as is known in the art. Inlets for chemicals, such aspH-adjusting compounds, or additional feedstreams can be added. Thefluid being treated can also be brought into contact with other treatingmedia, such as activated carbon, in a separate treatment bed. In thealternative, other treating media can be interspersed with redox media.

The inventive system is potentially useful in any industrial facility orcommercial building using cooling towers. For example, many largebuildings use cooling towers to provide cool make-up air for their airconditioning systems. In addition to the foregoing, the system can finduse in other applications, such as boiler systems, chiller systems,quenching systems, and pre-conditioning systems used prior toion-exchange treatment. Installation of treatment system 10 in anexisting system is relatively simple, involving merely connecting theinlet and outlet piping to the reservoir, bringing power to a controlpanel, and running the backwash discharge to a sewer line.

Although the invention has been described in terms of specificembodiments and applications, persons skilled in the art can, in lightof this teaching, generate additional embodiments without exceeding thescope or departing from the spirit of the claimed invention. Forexample, while the invention has been described in terms of industrialuse, it can be adapted for any commercial or domestic use. Accordingly,it is to be understood that the drawing and description in thisdisclosure are proffered to facilitate comprehension of the invention,and should not be construed to limit the scope thereof.

What is claimed is:
 1. A process for treating fluid comprising the stepsof:filtering a fluid by physical filtration media to removeparticulates; and treating the filtered fluid by contact with afluidized redox media in a treatment bed in the form of a column, thetreatment bed having a reaction portion and a retention portion, theredox media being fluidized by flow of the filtered fluid runningcountercurrent to the effect of gravity on the column and being held inplace by a retention portion of the fluidized column, the retentionportion having a diameter which is greater than the diameter of thereaction portion.
 2. The process of claim 1 further comprising the stepof periodically reversing the flow of fluid through the physicalfiltration media to remove trapped particulates.
 3. The process of claim2 wherein the physical filtration media is sand.
 4. The process of claim1 wherein the redox media is a bimetallic alloy of copper and zinc. 5.The process of claim 4 wherein the alloy is a 50:50 mixture of copperand zinc.